Shock waves occur when the processes of reaching supersonic speeds (for the MFA is 1-10 km / s). This happens when an outbreak of a supernova, the dumping of the envelope, a collision between a gas cloud, the gravitational collapse of gas clouds, etc. In the front shock wave directional kinetic energy of motion rapidly becomes the energy of chaotic motion of particles. Sometimes the temperatures can reach huge values (up to a billion degrees inside the remnants of a supernova), the main energy is in the movement of heavy ions (ion temperature). Initially, the temperature easily electron gas is significantly lower, but due to Coulomb interaction ionic and electronic temperature is leveled. If the plasma has a magnetic field, the role of first violin in the equalization of the ion and electron temperatures assumes turbulence.
Penetrating radiation and cosmic rays
Cosmic rays and X-ray diffuse emission, the main sources of ionization of the interstellar medium, rather than UV, as might be expected. The particles of cosmic rays interacting with the environment, are the electrons to very high energy. This electron energy is lost in elastic collisions, and inelastic, resulting in ionization or excitation of atoms and ions. Epithermal electrons with energy less than 10 eV lose energy in elastic collisions, heating gas. Such a mechanism is extremely effective at temperatures 106. With 107 characteristic thermal velocity of electrons compared the thermal velocity of particles of low-energy cosmic rays and the heating rate decreases dramatically. Ionization and heating by means of soft diffuse X-ray of the hot gas does not differ fundamentally from the heating cosmic rays. All the difference in heating rate (from cosmic rays, it is an order of magnitude higher) and a much larger section of photoionization of internal shells of the X-rays.